There have been a number of ways proposed in the prior art for reducing this harmful electromagnetic flux. For example, increasing the air-gap length towards the end of the stator core reduces such core end flux. Reducing the relative axial length of the rotor with respect to the stator is another way to reduce the core end fringing flux. In addition, core-end stepping has been one of the commonly used techniques to modify the air-gap length in the core-ends to reduce the core end flux.
The amount of core-end stepping that can be used is limited, however, by the need to support the lamination “teeth” from flexing. Loose lamination teeth can flutter and break off causing machine failure.
All of these proposals for reducing the electromagnetic flux normal to the stator core-end that causes eddy current losses and heating in dynamoelectric machines also increase the excitation needs contributing to lower efficiencies and potentially a bigger thermal challenge.